Heavy machinery, such as off-highway trucking equipment, is commonly used in mining, heavy construction, quarrying, and other applications. Due to the substantial capital investment involved, tight tolerances with respect to the time allotted for completing tasks, and the expense of maintaining and operating heavy machinery, such as a mining truck, an entity can suffer significant monetary losses when the heavy machinery malfunctions. The complexity of modern heavy machinery often exacerbates this problem due to the need for skilled personnel to perform various tests on such machinery to trouble shoot such malfunctions. Even so, significant time is often spent locating the fault and then performing an appropriate repair.
One advance that has improved efficiency associated with the use of heavy machinery is the adoption of Alternating Current (AC) or electric drive systems. Electric drive systems typically require less maintenance and thus, have lower life cycle costs. When the heavy machinery malfunctions, however, the costs associated with determining the fault location and repair are often substantial.
Direct series electric drive systems for machines typically include a power circuit that selectively activates one or more drive motors at a desired torque. Each of the drive motors is connected to a wheel or other traction device that operates to propel the machine. A direct series drive system also includes a prime mover, for example, an internal combustion engine, that drives a power generator. The power generator produces electrical power that is often conditioned by a power circuit, and ultimately used to drive the motor. Conceptually, as the machine is propelled, mechanical power produced by the engine is converted into electrical power by the generator. This electrical power may be processed and/or conditioned by the power circuit before it is metered to the motors. The motors transform the electrical power back into mechanical power that drives the wheel and propels the machine.
One fault that can be difficult to detect and repair is the malfunction of diodes in a rectifier circuit disposed at the output of the power generator. Typically, when one or more of these diodes malfunctions, a power generator phase current imbalance results as current may recirculate back through the output winding of the power generator. This condition may reduce the amount of power output by the electric drive but not altogether cease. The entire machine must then be examined to detect the malfunction. This requires that the operator shutdown the machine and remove it from its task. Often, when a rectifier diode fails, the machine can still operate, although less efficiently, making it more difficult to detect that there is a fault and to determine where the fault exists. Such failures, if not detected early, may cause additional fault conditions to occur. This may ultimately lead to longer down-times of the machine.